The parallel combination of a valve regulated lead acid cell and supercapacitor for use as a hybrid vehicle peak power buffer

The performance of a standard, production valve regulated lead acid (VRLA) cell has been improved by paralleling with combinations of supercapacitors. The supercapacitors act to lower the source impedance of the combination providing a much-enhanced performance. Transient voltage swings are suppressed and the rms voltage is supported. Low temperature performance may also be improved due to the characteristics of the supercapacitor. These enhancements are described for various combinations of cell and supercapacitor under realistic hybrid vehicle power demands. A simple model is proposed and used to demonstrate supercapacitor size requirements for optimal current in the parallel cell